> At some point though LLVM began doing a valid optimization that valgrind was unable to recognize as valid, and that made its application useless for us, or at least too difficult to maintain.
What optimization was that? Some searching didn't turn up any relevant results (other than this article).
I couldn't quite remember either, and brson told me that https://github.com/rust-lang/rust/issues/11710 was probably it. Can't seem to find where it was actually finally disabled though.
"This is a known valgrind false positive and Rust already has a lot of suppressions for it. It's reported upstream on the LLVM bug tracker but is not really an LLVM issue, just a limitation of valgrind. LLVM is allowed to generate undefined reads if it can not change the program behavior."
[...]
"Just for the record, the undefined read doesn't change the behaviour because it's just a check whether free should not be called, i.e. either it jumps over the free call right away, or it performs the second check."
What optimization was that? Some searching didn't turn up any relevant results (other than this article).